A desire for increased fuel economy and reduced emissions has led to directed efforts in developing high pressure fuel injection systems and associated alternative fuel supply systems. Cleaner burning fuels are increasingly being used to replace more conventional diesel fuel. Alternative gaseous fuel systems deliver, for example, natural gas, pure methane, butane, propane, biogas, hydrogen and blends thereof. However, more broadly than these examples, in this disclosure “gaseous fuel” is defined as any combustible fuel that is in the gaseous phase at atmospheric pressure and ambient temperature. Since gaseous fuels typically do not auto-ignite at temperatures as low as liquid fuels, such as diesel fuel, small amounts of liquid fuel can be introduced into the combustion chamber to auto-ignite and trigger the ignition of the gaseous fuel. However developing systems which employ two or more different fuels have some unique challenges, including finding the physical space for all the components of such a system which may include, by way of example, two or more fuel injection valves for each engine cylinder, two or more high pressure fuel rails, one or more drain rails for taking away fuel that is drained from the control chambers of the hydraulically actuated fuel injection valves, and two or more fuel supply systems for supplying the fuels to the engine. In order to address the space challenges, systems have been developed which utilize a single injector to deliver two fuels separately and independently of each other into an engine combustion chamber at pressures high enough to overcome the pressure within the combustion chamber upon injection as disclosed in U.S. Pat. No. 6,073,862 by Touchette et al. and U.S. Pat. No. 7,373,931 by Lennox et al., both of which are incorporated herein by reference.
One of the challenges with this approach is providing consistent and uniform fueling pressure of the two or more fuels to the engine system for reliable engine performance and emissions control. When one or more of the fuels is in gaseous rather than liquid form, the ability to control the supply pressure of the fuel to the engine system becomes more challenging and requires tighter fluid handling and control systems than needed with fuels delivered in liquid form. Another challenge is keeping the different fuels separate when delivering the two or more fuels to the engine system. Again, this is even more challenging when one or more of the fuels is in a gaseous rather than liquid form, such as when a gaseous main fuel is employed within the same injector as a liquid pilot fuel. Leakage of gaseous fuel into liquid fuel supply lines is undesirable for a number of reasons, including the fact that it can result in faulty injection and/or ignition problems in the engine as well as result in an increase in unburned hydrocarbon emissions.
Preventing the leakage of a gaseous fuel into the liquid fuel cavities and channels of an injector can be prevented by maintaining the gaseous fuel pressure at a predetermined lower pressure compared to the liquid pilot fuel pressure. This pressure differential is referred to as the bias pressure, and this bias can be maintained by a pressure regulator which uses the liquid pilot fuel pressure as a reference pressure. Alternatively, the engine system can be calibrated based on a required gaseous fuel pressure and then the liquid pilot fuel pressure can be controlled to maintain a higher pressure than the gaseous fuel pressure. In both alternatives, a pressure regulator is associated with at least one of the systems fluid supply to maintain a pressure bias between the two fluids to prevent leakage of a first fluid into a second fluid.
The two or more fluid supply systems also may have other components, for example, valves for preventing the backflow of one fluid to another fluid's supply lines and tank, valves for venting the pressure in fluid supply lines, and valves for shutting down the fluid supply when needed; all of which take up additional space. A fluid control module, as disclosed in Canadian Patent 2,820,013 by Mark et al., was developed for controlling two fluid pressures going to separate fuel rails for injection into an engine while simultaneously controlling the desired pressure bias between the two fluids to prevent leakage of one fluid into the other within one or more injector(s). This prior art system design, as shown in FIG. 1, employs a passive venting mechanism 174 within the fluid control module that vents gas the moment the gaseous fluid pressure (which is intended to be the lower pressure fuel) exceeds the liquid fluid pressure within manifold body 130 of the fluid control module in order to maintain the pressure bias and prevent fluid contamination within the one or more injector(s). This system is effective in maintaining a pressure bias but it is designed to provide an ample margin of safety to prevent gaseous fuel from leaking into the liquid fuel. Nevertheless, because the two fluids pressures can fluctuate dynamically between the fluid control module and the fuel injectors this approach can lead to unnecessary venting of gaseous fuel. That is, because the control of the pressure bias is within the fluid control module which is removed some distance from the fuel injectors, where the fluid pressures, and more importantly, the pressure bias between the two fluids needs to be maintained, namely across match-fits between moving parts inside the injector(s). Unnecessary venting results in fluid loss to the system, and if not recovered in some way, gaseous fuel is released into the atmosphere.
This can be better understood, by reviewing the prior art fluid control module, shown in FIG. 1, which has a first fluid supplied to manifold body 130 through first fluid manifold inlet 124 and is directed through check valve 154 and shut-off valve 140 to pressure regulator 170 through first fluid pressure regulator inlet 126. The second fluid, acting as a pressure reference fluid, is supplied to manifold body 130 through reference fluid manifold inlet 142 which is fluidly connected to pressure regulator 170 through second fluid pressure regulator inlet 128. Second fluid pressure regulator inlet 128 is also in fluid communication with reference fluid manifold outlet 148. Pressure regulator 170 is designed such that it delivers the first fluid at a predetermined pressure bias compared to the second reference fluid pressure through first fluid pressure regulator outlet 136 and then out from manifold body 130 at first fluid manifold outlet 138. The first fluid pressure can also be reduced in the system by opening service valve 120, which vents fluid from manifold vent outlet 134 via vent line 132.
Prior art pressure regulator 170 is a dome loaded self-venting regulator (DLSR) having a pressure regulator valve component 172 and a passive vent valve component 174. Pressure regulator 170 links the two fluid pressures and controls the pressure bias between the two fluids so that the first fluid pressure, which can be in liquid and/or gaseous form, is controlled by the second fluid pressure, which can also be in liquid and/or gaseous form. In the illustrated prior art example in FIG. 1 the gaseous fuel is the first fluid controlled by the liquid second fluid. When the second fluid pressure moves up or down, the first fluid pressure moves up or down with the second fluid pressure by employing a mechanically set bias.
Pressure regulator 170 is designed such that the first fluid vents through passive vent valve 174 whenever there is a drop in the second fluid pressure below that of the first fluid pressure. When this occurs, the first fluid is directed from passive vent valve 174 to vent through vent line 132. In systems where the second (reference) fluid rises and falls gradually in pressure over time or when there is a large pressure bias between the two fluids, the reference pressure rarely drops below that of the first fluid pressure and the passive vent valve remains closed most of the time. However in systems where either the second fluid pressure drops quickly, the first fluid pressure rises quickly, or there is a small pressure bias, it can be more frequent for the second fluid pressure to drop below that of the first fluid pressure, and when this happens, passive vent valve 174 responds automatically by opening and venting the first fluid to vent line 132 and manifold vent outlet 134 in order to quickly drop the first fluid pressure thereby returning the fluid pressures exiting manifold body 130 back to the preset pressure bias.
This passive venting of the first fluid from the fluid control module occurs any time the second fluid pressure is lower than the first fluid pressure, either due to a drop in the second fluid pressure at the pressure regulator or when there is an increase in the first fluid pressure downstream of the fluid control module. When the fluid control module is employed in a mobile multi-fueled engine system designed to operate in many different fueling modes and change between those modes smoothly and quickly, unnecessary venting of fluid from the prior art fluid control module can result, especially in systems where the first fluid is a gaseous main fuel and the second fluid is a liquid pilot fuel. One example of unnecessary venting of the prior art module can occur when the engine demand for fueling goes from a low fueling demand requiring low or no flow rate of a first fluid (main gaseous fuel) and a second fluid (liquid pilot fuel) to a high fueling demand mode. This can occur when moving from idle mode to high demand mode; for example, the initial tip in on the accelerator when starting up a hill can drop the second fluid rail pressure below that of the first fluid rail pressure leading to a passive vent. Another example of unnecessary venting of the prior art module can occur when oscillations within the injector cause the first fluid pressure to exceed that of the second fluid pressure at the fluid control module which also causes a passive venting of the first fluid.
Another problem with the prior art fluid control module configuration when it is employed in a mobile multi-fueled engine system is when the engine system is being run in a single fuel injection only mode. In this mode, injectors using one or more dynamic liquid fluid seals between separate fluid channels which normally act to keep the different fluids separate, will allow one fluid to flow through the injector into the other fluid rail and into the fluid control module potentially damaging the pressure regulator and contaminating the separate fluid supply lines. This can also result in venting of the second fluid, which can be a liquid fuel such as diesel, through the manifold vent outlet.
Accordingly, there is a need to provide an improved high pressure fluid control system and method for relieving fluid rail pressure while reducing unnecessary venting. Additionally there is a need to provide an improved fluid control module and method for relieving fluid rail pressure that isolates the pressure regulator from high rail back pressure.